1. Field of the Invention
The present invention relates to a method of interconnecting the frame grounds in a housing so as to suppress radiation noise from the cable between circuit boards, and an electronic equipment with a structure connected by the method.
2. Related Background Art
Conventionally, the frame grounds in a housing are interconnected, as shown in FIG. 9. More specifically, in a housing including circuit boards 2.sub.1 and 2.sub.2, the housing or plate metals 1.sub.1 and 1.sub.2 connected to the housing are connected as frame grounds FG to the board grounds via members 5.sub.1 and 5.sub.2 as means for reinforcing the board grounds so as to take a measure against radiation noise from the circuit boards 2.sub.1 and 2.sub.2. The circuit boards 2.sub.1 and 2.sub.2 are connected to each other by a cable 4 via connectors 3.sub.1 and 3.sub.2, and the cable 4 uses a shield cable as a measure against its radiation noise.
However, in the prior art, when the circuit boards 2.sub.1 and 2.sub.2 are connected by the cable 4, different plate metals 1.sub.1 and 1.sub.2 are often connected to the circuit boards 2.sub.1 and 2.sub.2 in consideration of the layout in the housing. FIG. 10 illustrates the state between such different plate metals 1.sub.1 and 1.sub.2, i.e., different frame grounds. When the circuit boards 2.sub.1 and 2.sub.2 are connected to different frame grounds FG1 and FG2, these frame grounds FG1 and FG2 normally have different ground potentials Vg1 and Vg2, and a potential difference Vgc between these ground potentials is called a common mode potential. When the circuit boards 2.sub.1 and 2.sub.2 connected to the frame grounds FG1 and FG2 with different ground potentials Vg1 and Vg2 are connected by the cable 4, a common mode current Ic owing to the common mode potential concentratively flows through the cable 4, and common mode noise is radiated from the cable 4. Such common mode noise cannot be sufficiently shielded by the shield cable, and it is very difficult to solve this noise problem.